1. Field of the Invention
The present invention relates to a brush cleaning apparatus that efficiently cleans disk-shaped objects, for example, semiconductor wafers (hereafter simply referred to as wafer) and a cleaning system for the disk-shaped objects that uses the brush cleaning apparatus as a part thereof.
2. Description of the Prior Art
In semiconductor device fabrication processes, impurities and foreign matters adhered on the surface of a wafer, on which, for example, chemical impurities or particles are usually attached just after the wafer has been finished with a polishing process, have an adverse influence on the performance of semiconductor devices therefrom.
A cleaning operation is therefore indispensable in processes for producing wafers. And a variety of cleaning methods are available in the cleaning operation for a process for producing wafers, which are most broadly classified into the two groups of physical methods and chemical methods.
In the physical methods, included are a method in which impurities stuck on the surface of a wafer are directly removed by the mechanical action of a cleaning brush, another method in which a pressurized liquid is shot in a stream onto part or all of the surface of a wafer from a jet nozzle and thereby the impurities are removed off, and still another method in which impurities stuck on the surface of a wafer are removed off by application of ultrasonic wave energy in a condition that the wafer to be cleaned is immersed in a liquid, where ultrasonic wave is produced with a piezoelectric transducer installed under water.
In the chemical methods, impurities stuck on the surface of a wafer are chemically decomposed into constituents to be removed by the powers of chemicals or enzymes. In the meantime, both of the methods may be combined so as to improve the total cleaning capacity.
Among the above mentioned cleaning methods, the brush used cleaning method or simply brush cleaning method is effective in removing impurities such as particles attached on the surface of a wafer and therefore the brush cleaning method is well used in cleaning processes for wafers.
There is a traditional brush cleaning apparatus, which is cleaning both the surfaces of a wafer at a time with a pair of brushes, as the wafer is being turned about its center. In this type of brush cleaning apparatus, however, it takes a longer period of time for the whole surfaces of the wafer to be cleaned, since the peripheral area of either surface has a shorter period of time to contact with the brush than the central area and, what's worse, the very periphery and its neighbor are unfavorably restricted in cleaning action with necessity of mechanically supporting the wafer by the periphery in rotation thereof.